This study addresses ethnic matching of mental health clients with practitioners and the relationship of such matching to utilization of mental health services in the public sector. The literature contains many studies of ethnic matching, but few of sufficient scope, rigor, and relevance to service systems in the real world of practice to provide a reliable foundation of knowledge. In its approach to evaluation of the impact of ethnic matching, the present study will improve in several respects upon others. Specifically, it will: (1) evaluate ethnic-based matching, and two kinds of mismatching (pairing of an ethnic client with a white practitioner; pairing an ethnic client with a practitioner from a minority group other than that of the client); (2) consider the intensity (proportion of matched sessions) of ethnic matching; (3) distinguish between ethnic-based matching and language-based matching; (4) distinguish between matching at the level of the practitioner and the program or subprogram; and (5) simultaneously consider three major ethnic groups along with whites, (6) focus on utilization of specific types of services, and the possibility of substitution of less costly services for more costly ones. These aspects of matching will be addressed in a research design that features large samples of clients and clinicians, and specifies a theory-based multivariate model of utilization. Data for the study will be taken from the Mental Health Billing Information System (MHBIS) in use in Santa Clara County, and the City and County of San Francisco, California. Information on clients, clinicians, and programs will come from fiscal year 1987-1988 from these identical management information systems. these sources will provide data on large nonduplicated samples of minority and white clients. Several specific questions will be studied: (1) What is the relationship of ethnic matching of outpatient clinician and client (match vs. mismatch with white practitioner or mismatch with minority practitioner) to: utilization of specific types of services (outpatients, case management, hospital, emergency, locked, residential); substitution of less costly for more costly forms of service, and status at termination (successful vs. withdrew/unilaterally discharged vs. other)? What is the relationship of outpatient linguistic matching to these outcomes? What is the relationship of outpatient program matching (assignment to ethnic-focused program vs. other program) to these outcomes? (2) How is the relationship between each type of matching and these outcomes affected by adjustment for predisposing variables (client gender, age, marital status, education, employment), access variables (client income, insurance coverage; clinician gender, age, professional status, years training), and need (GAS rating and DSM III-R diagnosis)? Results from the study will be of use to policymakers, theorists, and practitioners. Policymakers will gain objective information as they consider gains and losses in minority utilization that result from an emphasis on various types of matching. Theorists can learn about the real world implications of matching as they seek to understand mental health in crosscultural context. Clinicians can better evaluate their strengths and weaknesses as providers of mental health service in considering opportunities for continuing education and making decisions about composition of their caseloads.